1. Field of the Invention
The present invention relates to a recording head for recording desired images on a recording medium, a substrate for use of a recording head, and a recording apparatus. The present invention is applicable to an apparatus, such as a printer that records on paper, thread, fiber, cloth, leather, metal, plastics, glass, wood, ceramics, or the like, a copying machine, a facsimile equipment with communication systems, a word processor with a printing unit. Further, the invention is applicable to the recording system for industrial use, which is arranged by combining various processing devices complexly. Here, the term “recording” used for the present invention is not only applied to the provision of meaningful images, such as characters and graphics, for a recording medium, but also, applied to the provision of the images which are not meaningful, such as patterns, for the recording medium.
2. Related Background Art
For the conventional recording head, there are a thermal head that records by transferring heat to an ink ribbon or a thermosensitive paper using heat generating elements, an ink jet head that records by discharging ink using piezoelectric elements. Hereunder, the description will be made of an ink jet head by exemplifying the one that records by discharge ink using heat generating elements.
With heat and other energy given to ink, change of states is created in ink, which is accompanied by abrupt voluminal changes (creation of bubbles). Then, ink is discharged form discharge ports by the active force exerted by such change of states. The ink thus discharged is allowed to adhere to a recording medium for the formation of images. This is called an ink jet recording method, which is conventionally known as the so-called bubble jet recording method. As disclosed in the specification of U.S. Pat. No. 4,723,129, and others, the recording apparatus that adopts this bubble jet recording method comprises, in general, the discharge ports that discharge ink; the ink flow paths which are communicated with the discharge ports; and recording elements servicing as energy generating means, which are arranged in the ink flow paths to discharge ink, respectively.
With the recording method of the kind, high quality images can be recorded at high speeds with a lesser amount of noises. At the same time, the head that performs this recording method makes it possible to arrange discharge ports in high density therefor. As a result, among some others, this head has an excellent advantage that images are recorded in high resolution with a smaller apparatus, and also, color images can be made easily. With such advantages, the bubble jet recording method has been widely unutilized in recent years for a printer, a copying machine, a facsimile equipment, and many other office machines and equipments. Further, it has begun to be used for textile printing systems, and some others for industrial use.
Now that the recording elements that generate energy for discharging ink are manufactured by use of the semiconductor manufacturing processes, the conventional head which has been made by the utilization of the bubble jet technologies and techniques is structured in such a manner that a substrate is formed by arranging recording elements on an elemental base plate formed by a silicon base plate, and that a ceiling plate formed by polysulfone or some other resin or glass or the like, which is provided with grooves, is bonded with such substrate to provide ink flow paths.
Also, by the utilization of the elemental base plate being formed by the silicon base plate, not only the recording elements are formed on the elemental base plate, but also, the driving circuit that drives the recording elements, the temperature sensor which is used to control the temperature of the recording elements, the driving controllers, and some others are arranged thereon. FIG. 15 shows one example of an elemental base plate of the kind.
In FIG. 15, there are formed on the elemental base plate 1001, the heater group 1002 having a plurality of heat generating elements (recording elements) 1005 formed by resistive elements that give thermal energy for use of ink discharges, which are arranged in parallel; a driving circuit 1003 having a plurality of transistors 1008 for driving each of the heating elements 1005, which are arranged in parallel; a control circuit 1004 for controlling each of the transistors 1008 on the driving circuit 1003; and input terminals 1007 for receiving image data, each kind of signals, and the like from outside. Also, for the elemental base board 1001, a temperature sensor that measures the temperature of the elemental base plate 1001 or a sensor 1006, such as a resistance sensor, for measuring the resistive value of each of the heat generating elements.
The control circuit 1004 comprises shift registers that outputs to the driving circuits 1003 the image data which are received serially from outside; the latch circuits that store data provisionally and output them to the transistors 1008; a driving control circuit that drives the sensor 1006, and controls the width of pulses to drive the heat generating elements 1005 in accordance with output from the sensor 1006. In this respect, the control circuit 1004 may be arranged to output image data individually or may be arranged to divide the heater group 1002 into plural blocks and output image data per unit block, among some others. In this manner, a plurality of shift registers are arranged for one head, and then, the image data transmitted from the ink jet recording apparatus are allotted to a plurality of shift registers, thus making the printing speed higher with ease.
As the sensor 1006, a temperature sensor that measures the temperature in the vicinity of the heat generating elements, a resistance sensor that monitors the resistive value of the heat generating elements, or the like is used.
As regards the discharge amounts in terms of the liquid droplets to be discharged, it is conceivable that the discharge amount is related mainly to the bubbled value of ink. the bubble value of ink changes depending on the heat generating elements 1005 and the circumferential temperature thereof as well. The temperature of the heat generating elements 1005 and that of the circumference thereof are measured by the temperature sensor. In accordance with the result thus obtained, the pulses, which gives energy only in an intensity small enough so as not to allow ink to be discharged (preheat pulses), are added before applying the heat pulses that enables ink to be discharged. Then, it is practiced that the pulse width of such preheat pulses or the output timing is controlled to change for adjusting the temperatures of the heat generating elements 1005 and the circumference thereof in order to maintain the image quality by discharging ink droplets in a specific amount.
Also, as regards the energy required for bubbling ink in terms of the heat generating elements 1005, the energy can be expressed by the product of the input energy per unit area which is needed for the heat generating elements 1005 and the area of the heat generating elements 1005, provided that the condition of the heat radiation is constant. In this way, the voltage applied to both ends of each heating element 1005, the electric current running on each heat generating element 1005, and the pulse width should be set only at the value at which the required energy is obtainable. The electric current running on each of the heat generating elements 1005 has different resistive value of the heat generating element 1005 depending on each lot or each elemental base plate 1001 due to the varied film thickness of the heat generating elements which may be obtained in the manufacturing process of the elemental base plate 1001.
Therefore, if the resistive value of the heat generating element 1005 is greater than the set value, the value of running electric current becomes smaller, provided that the width of the applied pulse is constant. Then, the amount of the input energy of the heat generating element 1005 becomes insufficient to make it impossible to bubble ink appropriately. On the contrary, if the resistive value of the heat generating elements 1005 is made smaller, the value of electric current becomes greater than the set value even if the same voltage is applied. In this case, an excessive energy is generated by each of the heat generating elements 1005 to bring about a possibility that the heat generating elements 1005 are damaged or the life thereof is made shorter. Now, therefore, the resistive value of each of the heat generating elements 1005 is monitored by means of resistance sensor at all the time. Then, it is arranged that the width of heat pulses is changed in accordance the value thus obtained so that substantially a specific energy is applied to each of the heat generating elements.
As described above, the conventional ink jet head which is provided with the elemental base plate, there is a need for the provision of two kinds of voltage supply sources for supplying a voltage for use of the heat generating elements, and a voltage for use of the control circuit that drives it. These voltages are supplied from the main body of the ink jet recording apparatus.
In order to supply the source voltage to the ink jet head which is mounted on a carriage that moves along the surface of a recording medium for printing, the ink jet head and the main body of the recording apparatus is connected by means of a comparatively long cable, such as a flexible base plate. As the structure is thus arranged, the voltage for heater application which is supplied to the ink jet head may be caused to drop in some cases if many numbers of heat generating elements are driven at a time.
For the conventional ink jet head, therefore, the voltage that should be applied to the heat generating elements is set at a value higher than the voltage required for the performance of discharge (hereinafter referred to as the discharge voltage) with such a voltage drop in view. As a result, the durability of the heat generating elements is subjected to being deteriorated.
Also, noises tend to be superposed on the signals or voltages transmitted through the cable, such as flexible base plate. There is a possibility that the heat generating elements are damaged by spiking noises or the durability thereof is deteriorated if not damaged.
In recent years, there have been heavy demands on the high quality image output by an ink jet recording apparatus along with the widening fields of various products, respectively. At the same time, it is required that the recording speeds are improved. As a result, the number of nozzles (ink flow paths) should be increased for discharging ink, and the recording cycle should also be shortened. Then, the width of driving pulses should be shortened when applied to each of the heat generating elements, and at the same time, the number of recording elements should be increased for a simultaneous driving.
However, the voltages that are applied to the heat generating elements of the conventional ink jet head are the fixed ones. Therefore, when controlling the ink discharge energies corresponding to the kinds of ink or the sizes of each heat generating element, there is no other way than to control it only by changing the width of heat pulses. With the structure thus arranged, the pulse width cannot be shortened at all. It is, therefore, difficult to deal with the requirement of higher speeds (the discharge frequency being 10 kHz or more, or 20 kHz or more in some cases, for instance), and the provision of multiple nozzles which should be required as well.